The small intestinal surface brush border enzymes sucrase-isomaltase and lactase will be purified to homogeneity from human and rat intestine and fully characterized biochemically. Study of the turnover of these enzyme will be carried out by aid of quantitative immunoprecipitation using a monospecific antibody to each glycoprotein. The study of the half life of the proteins will be correlated with the type of nutrients in the diet and will also be related to diseases where these enzynes are known to be altered such as diabetes or chronic diarrhea. Study of the mechanism of insertion of the glycoproteins into the intestinal brush border surface membrane will be carried out using radiolabel techniques that will allow labeling from the intestinal lumen, intracellular space, and hydrophobic region of the membrane. The enzymes will then be isolated by quantitative immunoprecipitation, treated with trypsin or cyanogen bromide and the peptide fragments monitored for identification of the labeling material. In this manner, it is expected that it will be possible to determine the regions of the biologically active protein that are confined to certain aspects of the membrane. The overall goals of the project relate to the elucidation of the mechanism whereby dietary carbohydrates are hydrolyzed at the intestinal lumen-cell interface and the manner in which these enzymes are regulated in health and altered in disease. BIBLIOGRAPHIC REFERENCES: Gray, G.M. Carbohydrate digestion and absorption. Role of the small intestine. New. Eng. J. Med. 292:1225-1230, 1975. Conklin, K.A., Yamashiro, K.M. and Gray, G.M. Human intestinal sucrase-isomaltase. Identification of free sucrase and isomaltase and cleavage of the hybrid into active distinct subunits. J. Biol. Chem. 250:5735-5741, 1975.